Fusion protein technology, i.e., expressing in a host cell a target protein fused with a protein tag, confers several advantages. For example, many protein tags increase water-solubility and facilitate purification of their fusion partners. Further, several protein tags serve as protein chaperons to guide proper folding of the target proteins fused to them, thereby increasing the yields of the target proteins in native form.
One the other hand, fusion protein technology is disadvantaged in that protein tags often interfere with the structural or functional properties of the target proteins. Thus, they need to be removed via, e.g., chemical or enzymatical cleavage, from fusion proteins to release the target proteins. Cleavage of a fusion protein to remove the protein tag remains a major challenge in fusion technology as imprecise cleavage would result in failure to recover a structurally intact target protein.